1. Field of the Invention
The present invention relates to a direct injection spark ignition internal combustion engine in which fuel is injected from one side of a cylinder bore toward the cylinder bore wall on the opposite side of the cylinder bore such that the injected fuel rides on an intake air flow during an intake stroke, and a fuel injection control method for such an internal combustion engine. More specifically, the present invention relates to a direct injection spark ignition internal combustion engine that reduces dilution of oil by fuel that strikes the cylinder bore wall, and that effectively utilizes the latent heat of fuel evaporation and the effect of disturbance by a fuel jet, during homogeneous combustion to improve the homogeneity of an air-fuel mixture, and a fuel injection control method for such an internal combustion engine.
2. Description of the Related Art
In a conventional gasoline direct injection engine in which fuel is injected from one side of a cylinder bore (for example, between two intake valves) toward the cylinder bore wall one the opposite side such that the injected fuel rides on an intake air flow during an intake stroke.
In this type of engine, it is desirable to more or less reduce the penetration of fuel spray in order to improve the homogeneity during homogeneous combustion and reduce generation of low-temperature smoke and hydrocarbon (HC). It is also desirable to increase the injection angle (installation angle) in order to reduce fuel adhesion to a piston.
With this in view, there is proposed a related art providing a fuel control device for a direct injection type spark ignition internal combustion engine that includes a fuel injector for directly injecting fuel into a combustion chamber and an ignition plug, and that performs stratified operation, in which fuel is sprayed in a concentrated manner toward the vicinity of the ignition plug, and homogeneous operation, in which fuel is sprayed in a distributed manner all over the combustion chamber, according to engine operating conditions. This fuel control device includes multiple injection control means for allowing a plurality of fuel injections during each cycle in the homogeneous operation. The multiple injection control means varies time intervals between injections and injection amounts for the respective injections according to the engine speed and load. (See Japanese Patent Application Publication No. JP-A-2002-161790, for example.)
Also, there is proposed a related art providing a fuel injection device for an engine having an ignition plug disposed in the center of a combustion chamber when viewed in the cylinder axis direction and a fuel injector for injecting fuel provided to face the combustion chamber. In the fuel injection device, a fuel injection port of the fuel injector is disposed at a periphery of the combustion chamber on an intake port side when viewed in the cylinder axis direction. The fuel injection device is provided with injection control means for controlling the fuel injector such that fuel injection is started during a first half of an intake stroke of the cylinder, and such that a plurality of multiple fuel injections are performed during an intake stroke. (See Japanese Patent Application Publication No. JP-A-10-159619, for example.)
In the former related art, however, the penetration of fuel spray is limited. Also, fuel may ride on an intake air flow at an excessive speed and thus an increased amount of fuel collides against the cylinder bore wall. The fuel adheres to the cylinder bore wall and flows via a piston ring into an oil pan, where the fuel dilutes oil, which deteriorates the engine quality.
In the full-load range where the homogeneity of air-fuel mixture and the utilization of the effect of latent heat of fuel evaporation and the effect of disturbance by a fuel jet are both desirable, in particular, fuel injection timing in the range where the piston speed is maximum is unavoidable.
In the related art according to Japanese Patent Application Publication No. JP-A-10-159619 mentioned above, fuel is not injected during an intermediate period of an intake stroke. However, because the absence of fuel injection is not because of an injection prohibition period set for positive prohibition, fuel is highly likely to be injected even during an intermediate period of an intake stroke if injection of a larger amount of fuel is demanded, which may lead to the problem of oil dilution described above.